This application relates to magnetic materials and their use in tags or markers in systems for security tagging, anti-pilferage, article location and article identification.
Anti-pilferage tags or markers are applied to articles of commerce in order to protect them from theft from the sale premises. Similar tags are applied to articles or persons for stock control or identification purposes, being detected when the articles or persons pass or attempt to pass preselected detection stations. The markers are also attached to fixed articles which may be concealed, encased or covered over by other structures or materials; in this case, the articles to which the markers are attached are located by the use of a portable marker detector.
In order to achieve the desired magnetic properties, and in order to minimise the overall size and manufacturing cost of the marker, it is advantageous to manufacture magnetic elements of the marker in the form of thin sheets, foils, or films. There are usually two components to such markers. One is an `active` magnetic material which has soft magnetic properties, i.e. high permeability and low coercive force (under 100 Am.sup.-1). The second component is a semi-hard or hard magnetic material, which is often referred to as a `deactivation` material, and which has a medium permeability and a medium to hard coercive force (over 1000 Am.sup.-1). The active material produces the detectable signal, and the semi-hard or hard component produces a switchable dc magnetic field which biases or suppresses the response of the active material under appropriate conditions. Both types of material are currently produced using comparatively expensive alloys and processes to achieve the special magnetic properties required. Examples of current alloys are Vacozet, Vitrovac and Crovac from Vacuumschmeltze in Germany; and Arnokrome from Arnolds in the USA. We have identified materials and processes which may result in cheaper production of the magnetic components.